i was there in Sept 2004.
My top tips for lowering costs:
1. Stay in hostels. You can find listings in Lonely Planet(avoid the ostentatious chinese-run hotels). I stayed in cheapest, most run-down hostel for the first day in Lhasa, but couldn't stomach it as their shared communal toilets did not have working flushes and s*** was just piling all over the place. Transfered to a much better place (Banak Shol) the second day. It had MUCH better rooms, and a rooftop restaurant with a totally kick-ass view. You could even see the Potola Palace. Some costs are just not worth saving. It's only a few dollars difference anyway.
2. Travel in a small group of 3-4 persons. This will reduce costs in two ways: accomodations (room sharing) and transport. Sharing costs for transport in particular, is the best way to save money. As you're going to be there for 2-3 weeks, you are definitely going to be travelling out of Lhasa. And the immense distances mean high transport costs. If you can find travel kakis from Singapore, that would be the most convenient. If not, the hostels are always a great place to find people going to similar destinations. Just check the hostel noticeboards. The hostel (Banak Shol) I stayed is had its own travel agency with their own vehicles and drivers. The staff was very helpful in ensuring we were able to arrange the trips we wanted (we did some prior research and knew exactly where we wanted to visit in Tibet). Ensure both sides understand where you are going to be visiting (including any side trips or locales you want to see along the way) so that there will be no arguments with the driver DURING the trip.
3. The largest cost will come from transport to and from Tibet (airfare). So spend some effort in trying to secure the cheapest flights you can find from Singapore. It could be a difference of a couple of hundred dollars. I flew into Chengdu and settled travel permits there before flying into Lhasa, Tibet. Stayed in a very nice hostel in Chengdu (run by a Singaporean and his Japanese wife. It's called Sim's Cozy Guesthouse. Check it out on the web). They will be able to settle the flight and permits into Tibet for you.
4. Don't stinge on things like entrance fees and jeeps. The travel agencies in Lhasa offer different types of jeeps, and it's totally worth it forking out a bit more money to get a newer, smoother model. Remember you're gonna be spending most of your time travelling in that jeep. Besides, splitting the extra cost amongst 3-4 persons will make it very much more affordable. And treat your driver well. They will probably be able to converse with you in Mandarin. If you can find out more about his background, his history, it might make a more interesting trip. And they can point out things that you might otherwise miss.
5. Most importantly, give yourself at least three days to acclimatise to the altitude in Lhasa. I was a bit over-eager and rushed off on a trip to Nam Tso Lake by the third day, and suffered the worst headaches of my life. And that's really something for a person who suffers from migraines. I think it probably took me about a week to finally acclimatise and for the headaches to ease.
